Don't go with a cheap motherboard with that CPU + GFX combo, it will severely limit their capabilities. Find something full ATX size, with high speed RAM slots, and an upper-end chipset like an AMD 990FX.

What is relatively cheap? You gotta know what you want to do with your motherboard to select the right one. Overclocking, have enough slots for your RAM, slot to match your video card, expansion slots - form factor to fit your case, some cheaper ones only have PCIE which means you have to get wireless cards or anything else new. Try geeks.com or newegg.com to select an appropriate mobo.